First-principles prediction of outstanding thermoelectric performance in out-of-plane p-doped GeSe*

The record-breaking thermoelectric performance of tin selenide (SnSe) motivates the study of analog compounds such as germanium selenide (GeSe) that have the same crystal structure. Using extensive first-principles calculations of hole-impurity, hole-phonon, and phonon-phonon scattering, we investigate the thermoelectric transport properties of the orthorhombic (Pnma) phase of p-doped GeSe. Due to its ultralow total thermal conductivity, high Seebeck coefficients, extremely low Lorenz numbers, and relatively large band gap, we predict outstanding thermoelectric performance in GeSe crystals over a broad range of temperatures. In particular, the out-of-plane direction in GeSe exhibits comparable performance to SnSe at temperatures above 500 K. We extend the analysis to 900 K in order to determine the optimal hole doping to maximize zT. Our results, based on detailed first-principles calculations, are a strong motivation for continued experimental work focused on improving the efficiency of doping in GeSe to reach the optimal hole density.